The Myers-Briggs Type Indicator is a well known personality test. And now, just for fun, you can choose to specify your personality type in your TT profile.
Are you an idealist, a performer, a teacher, or a hostess, etc.? Are you one of the rare INFJs who make up just 1.5% of the world's population, or one of the more common ISFJs who make up 13.8%?
First read about the different personality types and then take the test to determine your type (see also alternate tests one and two).
Once you have established your type you can update your profile accordingly.
The results for all members who choose to take part are listed here: TT member personality types
Personally, I'm an ISTP. This is shared with John Malkovich, Mel Gibson, Noel Gallagher, Rowan Atkinson, Clint Eastwood, and James Bond.